2/10/2015. Adaptation and Natural Selection. Natural Selection

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1 We ve been talking a lot about adaptations and strategies : Water storage Drought tolerance Pollinator/plant matches Does this mean plants plan and have strategies? Does this mean plants strive to live in the mountains or desert? Do they make to do lists? Was there a design and implementation? The answer to these questions is: NO So what are adaptations? and how do they arise? Adaptations are features that provide some improved function. Production of a more intensely red flower that better attracts a hummingbird pollinator. The ability to more quickly produce fresh leaves after a desert rain. The ability to open stomata at night and store CO2 until the next day to save water while hotosynthesizing. Many of the things that impress us most in nature are adaptations. Most things we see in the human world which have clear functions were purposefully designed for that function. We correctly assume that there was some striving and planning that went into the conscious design. Early humans assumed the same about adaptations in nature. 156 years ago, a revolution in science showed that this intuitive idea was not true. How do adaptations arise in nature? Natural Selection 1

2 How does natural selection work? First, there must be variation in some trait of an organism (e.g., brown and green beetles). Second, there is differential reproduction (e.g., if green beetles are eaten more by birds, they will survive and reproduce less than brown beetles). Third, there is heredity (the surviving brown beetles have baby brown beetles color is genetic). End result: The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown. If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. Variation arises from small inherited modifications (mutations). These are shaped by survival. We say things like, the beetles are brown to avoid being eaten by predators. But it s really a shortcut for saying, beetles with genes for brown replaced other variants due to their ability to avoid predation. How does natural selection work? There must be variation in some trait of an organism (e.g., coat color in mice). The variation must have a genetic basis (the genetics of coat color is well understood). 2

3 How does natural selection work? There must be differential reproduction (in western AZ there are areas of sand and lava). Lava is dark, sand is light. How does natural selection work? Dark mice are more easily found and eaten by visually hunting predators on sand. Light mice are more easily found and eaten on lava. Years of such selection has resulted in genetically different dark mice being found only on lava and light mice only on sand. If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. Hawks vary genetically in how strong and sharp their talons are and how strong their foot muscles are. Hawks with less developed, weaker talons fail to catch their prey as often than hawks with well developed strong talons. Less food makes it harder for them to survive, produce healthy young, and feed them. Thus hawks with well developed strong talons pass on more genes for strong talons to the next generation. This active natural selection keeps the highly adapted talons working properly. Without this continuous selection this adaptation would fade away. This kind of natural selection was also responsible for originally forming the talons of hawks from weaker feet of ancestral birds that became better and better predators. 3

4 So natural selection results in adaptations Like the shape, color and nectar of a hummingbird flower. So is everything in nature an adaptation? No. Some things that are not adaptations: Vestigial structures features that were adaptations for the organism's ancestor, but that evolved to be non functional because the organism's environment changed. E.g., the eyes of cave fish Fish species that live in completely dark caves have vestigial, non functional eyes. When their sighted ancestors ended up living in caves, there was no longer any natural selection that maintained the function of the fishes' eyes. Fish with better sight no longer out competed fish with worse sight. Today, these fish still have eyes but they are not functional and are not an adaptation They are just the by products of the fishes' evolutionary history. Some things that are not adaptations: Non functional DNA doesn t seem to do anything. Mutations in this DNA get passed on to offspring have no obvious effect on the organism. The accumulate because they are not selected against. Some things that are not adaptations: The color of blood It's a by product of the chemistry of blood, which causes it to reflect red light. The chemistry of blood may be an adaptation, but blood's redness is not itself an adaptation. Some things that are not adaptations: An outdated adaptation. It might be an adaptation for a past environment and not the current one. For example, scientists have hypothesized that the chain fruits of cholla are actually an adaptation for seed distribution by large extinct mammals such as the gomphothere. If the hypothesis is correct, these fruit characteristics can no longer be considered adaptations for seed distribution. 4

5 Common Misconceptions about Natural Selection Natural selection cannot try to supply what an organism "needs." it is not a guiding hand Rather it is the mindless and mechanistic result of variation, differential reproduction, and heredity. It has no intentions or senses; it can t sense what an organism needs. Common Misconceptions about Natural Selection At the opposite end of the scale, natural selection is sometimes interpreted as random. Genetic variation resulting from mutations have random effects on an organisms survival and repro success. Mutations can be beneficial, neutral, or harmful. Mutations do not "try" to supply what the organism needs. In this respect, mutations are random whether a particular mutation happens or not is unrelated to how useful that mutation would be. But natural selection acts on that variation in a very non random way: genetic variants that aid survival and reproduction become more common than variants that don't. Natural selection is NOT random! Common Misconceptions about Natural Selection Some people think it applies to changes acquired do to struggling and developing in an individual life. Arnold s physical achievements aren t inherited. So they re not adaptations. Common Misconceptions about Natural Selection natural selection is all powerful and produces perfection. it s not and it doesn t! (the PBS fallacy) It produces things good enough to produce some genes in the next generation. No population or organism is perfectly adapted. Partly because of trade offs: e.g. growth rate vs WUE people may have genes for genetic diseases, plants may not have the genes to survive a drought, a predator may not be quite fast enough to catch her prey every time she is hungry. Common Misconceptions about Natural Selection natural selection is all powerful and produces perfection. It is limited by having to tinker with things that already exist Selection can work only with available variation. Common Misconceptions Natural selection guides species toward some goal. Natural selection is random. Natural selection involves a passing on of traits acquired during a life. Natural selection leads to perfect adaptation (the PBS fallacy). 5

6 The basic idea of evolutionary theory is that life has existed for billions of years and has changed over time. belief or fact? Scientists don t believe in evolution. Rather, they accept the theory of evolution, because There is overwhelming evidence for it. Simple inevitable sorting mechanism Extensive fossil evidence Scientists document evolution occurring in nature today Scientists do evolution in the lab. Many divergent lines of evidence converge to demonstrate that that life has existed for billions of years and has changed over time. The fossil record of long term evolution is vast and detailed. The fossil record of long term evolution is vast and detailed. Transition to horse (and Thoatherium) The fossil record of long term evolution is vast and detailed. The fossil record of long term evolution is vast and detailed. 6

7 Want to see fossil evidence of evolution? You are at the right place at the right time! Tucson Gem and Mineral Show Thousands of fossils for sale (but you can just look! ) Best bet: La Quinta Inn at I 10 & St. Mary's Rd (Behind the Shell Gas Stn.) Modern epidemiology tries to anticipate and overcome the rapid evolution of disease organisms. AIDS virus is so difficult to overcome because it evolves very fast it is multiple moving targets. new strain of flu are constantly evolving Viruses have very rapid mutation rate. They also can swap genes with other viruses. If 2 different viruses infect the same host, their genes can get jumbled up as they reproduce. Evolution? Mutation and gene swapping = heredity and variation Birds are the main hosts for flu viruses. But they have moved to pigs, horses and humans. Some of the heritable variations of flu have traits that let them survive and reproduce well in humans. Some have gene building enzymes that work well at human body temperature, which is a few degrees cooler than a bird s. So YES: variation, differential reproduction, and heredity evolution by natural selection. Flu evolves yearly Our immune system and new vaccines kill many genetic variants The surface proteins change shape through mutation, allowing some viruses to evade the immune system and anti flu drugs. Every year new vaccines must be developed to circumvent this rapid evolution. Some years especially virulent strains evolve. Some years the annual vaccine works better against the latest evolving strains. The 2009 H1N1 flu wasn t just a new strain of human flu involved a combination of bird, human and swine flus. While it killed young people more than most human flu strains, it has not been more severe than most human strains. But it can still evolve in the future. A H1N1 flu that evolved in 1918 caused ~50 million deaths worldwide. 7

8 Evolution of drug resistance Due to improper use of prescription drugs, not all bacteria are killed. Variants that are resistant to the drugs survive and reproduce and the bacteria become drug resistant A strain of Staphylococcus aureus evolved resistance to all penicillin type drugs. It is now widespread in hospitals. A new strain of gonorrhea resists all drugs. Evolution of drug resistance Same problem with pneumonia, tuberculosis and malaria. In 2009 scientists announced the discovery in western Cambodia of strains of malaria that have evolved resistance to the most effective malaria drug, artemisinin. Emerging major medical problem that can only be understood in terms of natural selection and evolution. Crickets on Kauai evolved silence to escape an introduced predator Male crickets sing to attract mates A fly with larvae that eat the crickets was introduced from North America. Between 1991 and 2001, the cricket population plummeted. This provided intense natural selection favoring any genetic variant that could resist the flies. in nature A mutation removes the male song. (they rub their wings together to make sound and the scraper was missing on the mutant). In 2003 the cricket population bounced back. But the crickets were all silent! Silent crickets evolved in 20 or so cricket generations! /10/ silent crickets.html Normal Genetic mutant Blue mussels on the Atlantic coast Similar story to crickets The mussels produce thicker shells in response to native crabs (they respond to a chemical the crabs emit). A non native Asian shore crab invaded the region around 1990 and began eating the mussels. But they couldn t respond to this new invasive crab. After 15 years they could. Adaptations to global warming Global temperature has risen roughly 1.53 F (0.85ºC) since

9 Adaptations to global warming Tucson temperature has risen roughly 3 F (1.7ºC) over the last century! Aside on public opinion about global warming 67% US adults believe there is solid evidence the earth is getting warmer. Only 44% believe it is due to human activities! Public opinion is way behind the science. People know about science issues in the public sphere but the depth of knowledge is not very high. People in general don t know much about bird flu, climate change, the ozone hole, health issues. People confuse climate vs. weather. Adaptations to global warming Many animals change in some non genetic way reproducing earlier in the spring for example or moving northward. This is not an example of evolutionary change. Adaptations to global warming But an number of species have adapted genetically: Canadian squirrels are breeding sooner in the spring, which allows them to hoard more pine cones for winter survival and next year's reproduction. Squirrels with genes for earlier breeding are more successful than squirrels with genes for later breeding. in nature Adaptations to global warming European Great Tits genetic variants with more flexible breeding time are increasing (and getting more food than less flexible variants). Adaptations to global warming European Blackcap British sub population has genetically changed to overwinter in Britain instead of migrating south. 9

10 Adaptations to global warming A North American mosquito has changed genetically to wait longer and gather more resources before going dormant. These changes seem small. But if you extrapolate to the millions of years life has been on earth, they are more than big enough to account for the dramatic shifts that have occurred during the history of life 10